Integrated microelectronic tubes having field emission cathode structures are well known as shown, for example, in U.S. Pat. Nos. 3,789,471, Spindt et al; 3,855,499, Yamada et al; and, 3,921,022, Levine. For such devices to function in the manner of vacuum tubes they must be fabricated with a high vacuum. However, to-date, no practical, commercially economical, means for producing such tubes with a high vacuum has been found. Consequently, substantially no use has been made of such tubes as vacuum devices.